---
title: "Linux Stdout Redirection To Dev Null File"
excerpt: "Disable or Modify System Firewall
, Impair Defenses
"
categories:
  - Endpoint
last_modified_at: 2022-04-05
toc: true
toc_label: ""
tags:
  - Disable or Modify System Firewall
  - Impair Defenses
  - Defense Evasion
  - Defense Evasion
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  - Endpoint
---

### :warning: WARNING THIS IS A EXPERIMENTAL analytic
We have not been able to test, simulate, or build datasets for this object. Use at your own risk. This analytic is **NOT** supported.


[Try in Splunk Security Cloud](https://www.splunk.com/en_us/products/cyber-security.html){: .btn .btn--success}

#### Description

This analytic looks for suspicious commandline that redirect the stdout or possible stderror to dev/null file. This technique was seen in cyclopsblink malware where it redirect the possible output or error while modify the iptables firewall setting of the compromised machine to hide its action from the user. This Anomaly detection is a good pivot to look further why process or user use this un common approach.

- **Type**: [Anomaly](https://github.com/splunk/security_content/wiki/Detection-Analytic-Types)
- **Product**: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- **Datamodel**: [Endpoint](https://docs.splunk.com/Documentation/CIM/latest/User/Endpoint)
- **Last Updated**: 2022-04-05
- **Author**: Teoderick Contreras, Splunk
- **ID**: de62b809-a04d-46b5-9a15-8298d330f0c8


#### Annotations

<details>
  <summary>ATT&CK</summary>

<div markdown="1">


| ID             | Technique        |  Tactic             |
| -------------- | ---------------- |-------------------- |
| [T1562.004](https://attack.mitre.org/techniques/T1562/004/) | Disable or Modify System Firewall | Defense Evasion |

| [T1562](https://attack.mitre.org/techniques/T1562/) | Impair Defenses | Defense Evasion |

</div>
</details>


<details>
  <summary>Kill Chain Phase</summary>

<div markdown="1">

* Exploitation


</div>
</details>


<details>
  <summary>NIST</summary>

<div markdown="1">

* DE.CM



</div>
</details>

<details>
  <summary>CIS20</summary>

<div markdown="1">

* CIS 3
* CIS 5
* CIS 16



</div>
</details>

<details>
  <summary>CVE</summary>

<div markdown="1">


</div>
</details>

#### Search 

```

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where  Processes.process = "*&amp;&gt;/dev/null*" by  Processes.process_name Processes.process Processes.process_id Processes.parent_process_id Processes.process_guid Processes.dest Processes.user Processes.parent_process_name 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `linux_stdout_redirection_to_dev_null_file_filter`
```

#### Macros
The SPL above uses the following Macros:
* [security_content_ctime](https://github.com/splunk/security_content/blob/develop/macros/security_content_ctime.yml)
* [security_content_summariesonly](https://github.com/splunk/security_content/blob/develop/macros/security_content_summariesonly.yml)

> :information_source:
> **linux_stdout_redirection_to_dev_null_file_filter** is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

#### Required field
* _time
* Processes.dest
* Processes.user
* Processes.parent_process_name
* Processes.process_name
* Processes.process
* Processes.process_id
* Processes.parent_process_id


#### How To Implement
To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you can use the Add-on for Linux Sysmon from Splunkbase.

#### Known False Positives
unknown

#### Associated Analytic story
* [CyclopsBLink](/stories/cyclopsblink)
* [Industroyer2](/stories/industroyer2)




#### RBA

| Risk Score  | Impact      | Confidence   | Message      |
| ----------- | ----------- |--------------|--------------|
| 36.0 | 60 | 60 | a commandline $process$ that redirect stdout to dev/null in $dest$ |


> :information_source:
> The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author. 

#### Reference

* [https://www.ncsc.gov.uk/files/Cyclops-Blink-Malware-Analysis-Report.pdf](https://www.ncsc.gov.uk/files/Cyclops-Blink-Malware-Analysis-Report.pdf)
* [https://www.trendmicro.com/en_us/research/22/c/cyclops-blink-sets-sights-on-asus-routers--.html](https://www.trendmicro.com/en_us/research/22/c/cyclops-blink-sets-sights-on-asus-routers--.html)



#### Test Dataset
Replay any dataset to Splunk Enterprise by using our [replay.py](https://github.com/splunk/attack_data#using-replaypy) tool or the [UI](https://github.com/splunk/attack_data#using-ui).
Alternatively you can replay a dataset into a [Splunk Attack Range](https://github.com/splunk/attack_range#replay-dumps-into-attack-range-splunk-server)


* [https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/malware/cyclopsblink/sysmon_linux.log](https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/malware/cyclopsblink/sysmon_linux.log)



[*source*](https://github.com/splunk/security_content/tree/develop/detections/experimental/endpoint/linux_stdout_redirection_to_dev_null_file.yml) \| *version*: **1**